This invention relates to a device for forming solder connections for example electrical connections between electrical conductors, method for forming solder connections using such a device, and the manufacture thereof. In particular the invention relates to a heat-recoverable device for forming solder connections.
The use of heat-recoverable articles for forming solder connections between electrical conductors is widely used. Such articles are described for example in U.S. Pat. Nos. 3,243,211, 4,282,396 and 4,283,596, the disclosures of which are incorporated herein by reference and are sold by Raychem Corporation of Menlo Park, Calif. under the trade mark "Solder Sleeve".
Typically such a device comprises a heat-recoverable sleeve containing a solder insert, generally in the form of a ring, and may contain one or more adhesive inserts. Such devices are typically used to connect insulated wires. The ends of the wires to be joined are stripped of insulation to expose their electrical conductors and inserted into the recoverable sleeve. The sleeve is then heated, causing it to recover, or shrink, into contact with the wires and the solder to melt and solder the exposed electrical conductors. Adhesive inserts, if present, are generally located each side of the solder insert and bond to the insulation of the wires to form an environmentally sealed splice or connection.
Solder connections can be made in-line in which a tubular sleeve having two open ends is used and the wires to be connected are inserted through each end of the sleeve. It is also possible to use a tubular sleeve closed at one end and open at the other to form a stub splice in which the wires to be joined are inserted into the open end of the heat-recoverable sleeve. A solder connection can be made between a pair of wires or a complex arrangement of a plurality of wires, such as in an automotive harness.
In assembling a harness a plurality of wires are inserted into a heat-recoverable soldering device and the resulting assembly is heated, for example, by an air gun, or the assembly may be placed in an oven or positioned within a heater, for example a belt heater, such as that described in copending commonly assigned U.S. patent application Ser. No. 07/641,374 filed Jan. 15, 1991, the disclosure of which is incorporated herein by reference.
Until the device has been heated to recover the sleeve and melt the solder and then cooled, it is possible for the wires to move relative to one another and to the solder insert resulting in a relatively poor electrical connection between the wires. For example a dry joint may result or there may be incomplete bridging of the solder between the conductors. It has been proposed to include within the sleeve a heat-recoverable polymeric ring which recovers at a temperature lower than the sleeve of the device. Once this preliminary temperature has been reached, the wires are retained in position during the remainder of the heating operation. Using this approach the wires are not retained in position until the heating operation has commenced. Positioning the assembly of wires and soldering device into the heater can cause the wires to dislodge from correct alignment. There is a need to retain the wires is position as the wire assembly is moved from the location in which it is assembled into the heating element as well as through the heating and cooling operation.